Continued Differential Ground Subsidence

We see evidence of continued differential subsidence of the land
surface over the crater in the geology and topography of the modern
land surfaces around the bay. First look at the geology. Notice that
the boundary between the older rocks (orange) and the younger rocks
(yellow) coincides with the position and orientation of the crater rim
on the three peninsulas that cross the rim. The cross section at the
bottom of the illustration shows how the older beds have sagged over
the more rapidly subsiding breccia, and the younger rocks have been
deposited in the resulting topographic depression. The topography also
reflects the differential subsidence. The Suffolk Scarp and the Ames
Ridge are elevated landforms (10-15 m high) located at, and oriented
parallel to, the crater rim.

Even the courses of the modern rivers in the lower bay region point to
the continued influence of differential subsidence over the crater.
Most of the rivers, like the Rappahannock, flow southeastward to the
Atlantic. But in contrast, the York and James Rivers make sharp turns
to the northeast near the outer rim of the crater. We infer that the
topographic depression over the crater has been maintained recently
enough to have been a significant determinant of the modern courses of
these rivers. This continued subsidence also may play a role in the
high rate of relative sea-level rise that is well-documented for the
Chesapeake Bay region. One of the locations of highest relative
sea-level rise is at Hampton Roads (the lower part of the James River),
located over the crater rim.